Cathode ray tube fabrication



United States Patent 3,357,767 CATHDDE RAY TUBE FABRICATION Paul C. Shatter, Seneca, Falls, N.Y., assignor to Sylvania Electric Products Inc., a corporation of Delaware No Drawing. Continuation of application Ser. No. 401,-

258, Oct. 2, 1964. This application Mar. 1, 1967, Ser.

5 Claims. (Cl. 316-19) Many of the conventional cathode ray tubes employed as image reproduction devices in color television applications incorporate a color screen in combination with a compatible grid or apertured structure such as the shadow mask type of construction. In such tubes, the screen which is generally disposed on the inner surface of the face panel of the tube, is composed of multitudinous dot, bar, or stripe formations of electron responsive green, blue, and red fluorescent phosphor materials. The respective fluorescent groupings constituting the patterned screen are formed in accordance with the number of electron guns to be utilized in the particular tube and with the respective apertured shadow mask employed.

Because of the large number of fluorescent material groups needed to produce a pattern suflicient to provide a high resolution picture, the process of forming the fluorescent pattern must be one which is capable of accurately forming discrete configurations to realize an imagery of desired color purity. By way of example, one conventional process utilizes a photoprinting technique wherein the inner surface of the viewing panel, having a coating of a light sensitive substance and a desired fluorescent phosphor material disposed thereon, is exposed to a specific point source of light; the beams of which pass through the apertures in the adjacently positioned mask to impinge upon the screen coating therebeneath. Subsequent development of the screen produces the first fluorescent pattern, which in this instance is a spaced array of phosphor dots capable of green fluorescence. This process is sequentially repeated with blue and red fluorescent phosphor materials to complete the production of the tri-color screen. In the exposure of each color portion of the screen, the point source of light is appropriately offset during the exposure operation to provide individual color emitting fluorescent material patterns which are discretely displaced from one another to form a repetitive plurality of color groupings comprising the screen.

When the apertured structure or shadow mask is of a foraminous nature, the resultant screen on the inner surface of the glass face panel is comprised of numerous triads of tangentially oriented green, blue, and red phosphor dots. Since these dots are photodisposed by light beamed through the foraminous mask, the dots are desirably in registry or alignment along the electron beam paths with the apertures of the shadow mask. Misregistry of the screen dots with the respective apertures in the.

mask has been a long standing problem in the art of color cathode ray tube fabrication. This has been infiuenced by an accumulation of variable factors including inefiiciencies in the electron gun structure such as inaccurate positioning of componential parts and misalignment of the guns, mask deformation, irregularities in screen deposition and defects in the convergence structure of the tube. With the advancement of the art and the increased efiiciencies of fabrication techniques, the pernicious effects of the above-mentioned factors have been greatly diminished. It was then found that the dot-aperture alignment is also deleteriously affected when the glass face panel, with the screen thereon, is sealed to the funnel portion of the tube. While the envelope or funnel may be of metal it is usually of glass, and the joining of the glass face panel thereto is conventionally accomplished by disposing a bead of frit sealing material therebetween and subjecting the panel-envelope structure to sufficient heat to consummate a seal. During the process of frit sealing the panel to the envelope, a temperature of approximately 445 C. is maintained for a time span of about one hour.

It has been discovered that the heat encountered by the glass face panel during the panel-envelope frit sealing process produces a permanent nonuniform transverse dimensional change in the glass supporting the screen dots and a variable degree of misregistry results which is differentially accentuated radially outward from the center of the panel. This effects a diminution of screen quality as it has been found that the dots comprising the screen may be nonuniformly shifted out of registry with the mask apertures. Measurements in 21-inch round panels, for example, show this variance in registry to range nominally from substantially zero at the center of the panel to a deviatory spread of from .002 to .005 inch in the peripheral portions of the panel. This aggravation has been found to be greater in rectangular shaped panels. In the finished tube this produces degrees of color impurity by allowing the electron beams to impinge portions of adjacent color dots or the interstitial spacings therebetween other than the intended primary target dots. For example, a screen photodisposed in spaced relationship to and in registry with a .foraminous mask having aperture diameters in the order of .011 to .012 inch has screen dot diameters in the order of .016 to .017 inch which are initially in registry with the apertures along the beam paths. In the finished tube the size of the electron beams impinging on the screen dots is likewise determined by the mask aperture size, however a slight misregistry is usually prevalent in some areas of the screen due to minute misalignment in the gun construction, the presence of adverse magnetic fields, etc. Thus, a predominantly radial shift in the panel dimensions =regardless of shape of the magnitude previously described may move the dots as much as .005 inch out of registry with the apertures, thereby permitting the electron beams to undesirably strike portions of tangentially positioned dots. A certain amount of misregistry in the finished tube can be overcome by the use of auxiliary electrostatic or magnetic field producing devices employed internally or externally of the tube, but this type of compensation does not afford adequate correction for the variable degrees of nonuniform misregistry resultant from the dimensional change of the glass panel. In many instances, finished tubes are discarded because of the noncorrective misalignment of the screen dots with the respective mask apertures.

Accordingly, it is an object of the invention to reduce the aforementioned disadvantages and to provide an improved color cathcde ray tube.

Another object of this invention is to improve, in the finished tube, the registry of the apertures in the mask with the corresponding phosphor pattern disposed on the inner surface of the fac panel.

A still further object is the provision of a method of producing improved screens for finished image reproduction devices.

The foregoing objects are achieved in one aspect of the invention by substantially finalizing the radial dimensions of the glass face panel of a cathode ray tube, prior Patented Dec. 12, 1967.

to the screen deposition thereon and the sealing thereof to a compatible envelope structure. This is achieved by subjecting the panel to a time-temperature combination at least commensurate with that encountered during subsequent panel-envelope sealing. This method incorporating a prebake heat treatment of the panel substantially finalizes the transverse dimensions of the glass panel in accordance with the respective time-temperature conditions; and the screen disposed thereon prior to scaling will substantially remain in registry with the mask in the finished tube.

For a better understanding of the present invention, together with other and further objects, advantages, and capabilities thereof, reference is made to the following disclosure and appended claims.

The glass comprising the light transmissive face panel may be of a nonbrowning potash soda barium formulation that will not discolor or darken under electron bombardment as, for example, Type 9019 as manufactured by Corning Glass Works, Corning, N.Y.

It has been found through extensive experimentation that a panel of the above-mentioned type of material press-formed and treated in accordance with th state of the art, can be selectively heat treated to effect a substantial finalizing of the transverse dimensions of the panel for discrete time-temperature combinations. The principles involved in this nonuniform dimensional change are not fully understood, but it is believed that a substantially permanent shrinkage of the glass takes place that is commensurate with the time-temperature factors involved. It is believed that slight variances of glass thickness and other minute variations in the pressed medium are factors influencing the nonuniformity of the transverse dimensional changes. For example, when a 21-inch round face panel of 9019 glass is heat treated or baked in an air atmosphere for approximately two hours, within an approximate temperature range of 440 to 450 C., a substantially transverse dimensional shrinkage takes place in the glass. This dimensional change progresses radially outward from the center of the panel in an increasing nonuniform manner, and therefore is greatest in the peripheral region. Measurements taken after the first hour of heating evidence a pronounced peripheral diametrical shrinkage averaging from .005 to .0075 inch, while the second hour of heating produces a reduced amount of shrinkage in the order .001 to .003 inch; i.e., during the two-hour period of the baking treatment a peripheral diametrical change in the order of .006 to .0105 inch is evidenced. Extension of the heating time at substantially the same temperature level produces a slight furtherance of lateral dimensional shrinkage of lessening significant amounts. Experimentation has shown that the two-hour baking treatment at an approximate 445 C. time-temperature combination produces at least a 90 percent dimensional finalizing in the transverse plane of the panel that will not substantially change when the panel is again subjected to substantially the same time-temperature combination. In this manner, a formed glass viewing panel, when baked at a temperature level substantially equaling that subsequently required to effect the frit sealing thereof to a compatibly formed tube envelope, for a time period substantially twice that required for frit sealing, will not undergo a substantial dimensional change during the subsequent fritsealing operation. Thus, an electron responsive screen disposed in registry with an apertured shadow mask on the substantially finalized panel will retain substantially initial registration alignment in the finished tube. a

In substantially rectangular shaped panels, as for example, those utilized in 25-inch rectangular cathode ray tubes, the dimensional finalizing treatment assumes even greater significance than that evidenced for round panels due to the differential transverse thickness of the rectangular panel medium.

It has been found that the baking treatment required to produce the desired dimensional stability of the glass face panel can be accomplished at any time prior to screen deposition.

In pursuance of a preferred embodiment of the invention, a controlled heat enclosure such as a conveyorized ir-atmosphere lehr is utilized to effect the desired baking of the panels. A lehr of this type has means for predeterminately controlling the temperature of the respective preheat, high te-mperature and cooling zones through which conveyor belt moves at a specifically controlled rate of travel. The panel positioned on individual supporting racks are placed in spaced relationship on the moving belt and sequentially conveyed through the preheat, high temperature and cooling zones in accordance with the time-temperature schedule to effect the desired dimensional changes within the panels. For example, when handling 21-inch round panels and 25-inch rectangular panels a two-hour baking at approximately 445 C. will produce the desired level of dimensional stability. It has been found that the baking temperature should be at least of a level substantially equaling that of the highest temperature encountered by the panel during subsequent processing, and the time element should at least substantially equal that required for the subsequent frit sealing process. Experimentation has shown that utilization of a time period at least twice that required for sealing substantially finalizes the transverse dimensions of the panel for subsequent equivalent heating conditions.

It has been found that, under certain frit material conditions, temperatures up to about 470 C. can be utilized for the frit sealing operation. Under such conditions the temperature of the panel baking treatment should substantially approximate that of sealing or be of a timetemperature combination to produce panel size finalization results at least equivalent thereto. If desired, a panel finalized, for example, at about 470 C. can be utilized in a lower temperature frit sealing operation.

After cooling, a plurally patterned dotted screen is suitably formed on the interior surface of the panel in alignment with an adjacently positioned foraminous mask. This is accomplished by means conventional to the art, as for example, by a photoprinting dot procedure whereby particles of a color phosphor deposited with a light sensitive resist material on the panel are discretely adhered by polymerization of the resist induced by beams of light passing through the multitudinous apertures in the mask. This photoprinting technique is repeated for the deposition of each electron responsive color phosphor comprising the plurally patterned screen.

The screened panel with the mask temporarily removed is conventionally processed by the addition of lacquering and aluminizing to provide improved reflective means, and by a subsequent heating treatment wherein the screened panel is subjected to a temperature level of about 410 C. for a time period of approximately forty-five minutes to remove the volatile chemicals therefrom. Since this chemical-removal-heating is of a lower temperature than the previous panel baking treatment, the dimensional stability of the panel is substantially retained. Thence, the panel with the mask repositioned therein in registry with the screen is positioned on the bonding surface of a compatible glass envelope funnel with a bead of sealing frit therebetween and sealed thereto by a lehr technique, wherein the envelope-funnel-panel structure is subjected to a time-temperature baking combination such as a time span of approximately one hour at a temperature level of about 440 to 450 C. The next sequential fabrication step involves sealing at least one electron gun within a suitable portion of the envelope, such as the neck region, to facilitate the desired electron beam relationship with the screen.

Final vacuum processing and sealing provides a completed tube having optimum registration of the pattern screen with the apertured mask that is in keeping with the alignment as initially disposed.

Thus, the occurrence of misregistration of the mask and screen during tube sealing and processing is substantially eliminated by effecting a transverse dimensional finalization of the tube panel prior to the deposition of the screen thereon that is in keeping with that found in the maximum time-temperature conditions encountered in processing. This improved method for fabricating a color cathode ray tube maintains optimum registration between the mask and the screen in the operating tube so as to produce a noticeable improvement in color purity.

While the invention has been described as applying to color cathode ray tubes, it is also applicable to other types of cathode ray tubes wherein a deleterious shift of the phosphor screen pattern results from heating after screening.

While there has been shown and described what is at,

present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

Iclaim:

1. In a color cathode ray tube having an annealed face panel with a patterned electron responsive screen formed on the interior surface thereof in registration with an adjacently positioned apertured mask and an envelope having at least one electron gun positioned therein to beam electrons through said mask to excite said screen, a method for fabricating said tube to insure lateral dimensional stabilization of said panel portion supporting said screen to provide improved registration between i said patterned screen and said mask, said method comprising the steps of: baking said annealed panel prior to screen forming at a time-temperature combination at least equaling that subsequently encountered to shrink the glass and achieve stabilization of the lateral dimensions of said previously annealed face panel; forming said patterned screen on the interior surface of said dimensionallystabilized panel in initial alignment and registration with said adjacently positioned apertured mask; heat sealing said panel, with said mask positioned therein, to said envelope;

heat sealing at least one electron gun in said envelope in electron beam relationship to said screen to effect a complete tube structure;and vacuum processing and sealing said tube structure to provide a completed tube having optimum registration of said patterned screen with saidapertured mask in keeping with the initial registration alignment therebetween. 2. A color cathode ray tube fabricating method according to claim 1 wherein said panel baking is at a timetemperature combination at least equaling that encountered 1 during said heat sealing of said panel to; said envelope.

3. A color cathode ray tube fabricating method according to claim 1 wherein said panel is of non-browning potash soda barium glass and wherein said panel baking is consummated at a temperature of substantially 445 centigrade for a time period of at least one hour.

4. In a color cathode ray tube wherein an annealed glass face panel of non-browning potash soda barium formulation has disposed thereon a patterned cathodoluminescent screen in registration withan adjacently positioned apertured mask, a heat treating method for substantially shrinking the glass and stabilizing the lateral dimensions of said previously annealed panel prior to screen depositions thereon, in a manner that said subsequently disposed screen will be in optimum registration with said apertured mask and will not shifttherefrom due to subsequent conventional heat to which the tube may be exposed, said method comprising the step of:

baking said annealed panel at a temperature level at least substantially equaling that of the highest conventional temperature subsequently encountered by said tube panel for a time span at least equaling that of said subsequent high temperature encounter.

5. A heat treating method for a color cathode ray tube panel according to claim 4 wherein the temperature level is substantially 445 centigrade for a time span of at least one hour.

References Cited UNITED STATES PATENTS 3,335,479 8/1967 Morrell 2925.13

RICHARD H EANES, JR., PrimarvExaminer. 

1. IN A COLOR CATHODE RAY TUBE HAVING AN ANNEALED FACE PANEL WITH A PATTERNED ELECTRON RESPONSIVE SCREEN FORMED ON THE INTERIOR SURFACE THEREOF IN REGISTRATION WITH AN ADJACENTLY POSITIONED APERTURED MASK AND AN ENVELOPE HAVING AT LEAST ONE ELECTRON GUN POSITIONED THEREIN TO BEAM ELECTRONS THROUGH SAID MASK TO EXCITE SAID SCREEN, A METHOD FOR FABRICATING SAID TUBE TO INSURE LATERAL DIMENSIONAL STABILIZATION OF SAID PANEL PORTION SUPPORTING SAID SCREEN TO PROVIDE IMPROVED REGISTRATION BETWEEN SAID PATTERNED SCREEN AND SAID MASK, SAID METHOD COMPRISING THE STEPS OF BAKING SAID ANNEALED PANEL PRIOR TO SCREEN FORMING AT A TIME-TEMPERATURE COMBINATION AT LEAST EQUALIZING THAT SUBSEQUENTLY ENCOUNTERED TO SHRINK THE GLASS AND ACHIEVE STABILIZATION OF THE LATERAL DIMENSIONS OF SAID PREVIOUSLY ANNEALED FACE PANEL; FORMING SAID PATTERNED SCREEN ON THE INTERIOR SURFACE OF SAID DIMENSIONALLY STABILIZED PANEL IN INITIAL ALIGNMENT AND REGISTRATION WITH SAID ADJACENTLY POSITIONED APERTURED MASK; HEAT SEALING SAID PANEL, WITH SAID MASK POSITIONED THEREIN, TO SAID ENVELOPE; HEAT SEALING AT LEAST ONE ELECTRON GUN IN SAID ENVELOPE IN ELECTRON BEAM RELATIONSHIP TO SAID SCREEN TO EFFECT A COMPLETE TUBE STRUCTURE; AND VACUUM PROCESSING AND SEALING SAID TUBE STRUCTURE TO PROVIDE A COMPLETED TUBE HAVING OPTIMUM REGISTRATION OF SAID PATTERNED SCREEN WITH SAID APERTURED MASK IN KEEPING WITH THE INITIAL REGISTRATION ALIGNMENT THEREBETWEEN. 